Fix Volume slider is captured in screenshot done in touchview mode

ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h

Index: ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h
diff --git a/ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h b/ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..381e2cba47e77dd887e1fdfe70fe58656d78a5cc
--- /dev/null
+++ b/ash/common/wm/maximize_mode/maximize_mode_screenshot_observer.h
@@ -0,0 +1,28 @@
+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_
+#define ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+class ASH_EXPORT MaximizeModeScreenshotObserver {
+ public:
+  virtual ~MaximizeModeScreenshotObserver() {}
+
+  // Notifies when screenshot is going to be taken by volume-down modifier +
+  // power button accelerator combinations. It receives the volume value that
+  // wants to be restored.
+  virtual void OnWillTakeScreenshot(int volume_percent) = 0;
+
+  // Notifies when screenshot is done. The implementation should restore the
+  // output volume.
+  virtual void OnDidTakeScreenshot() = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_WM_MAXIMIZE_MODE_MAXIMIZE_MODE_SCREENSHOT_OBSERVER_H_